1. Field of Endeavor
The present invention relates to the technology of gas turbines, and more specifically to a gas turbine of the axial flow type.
More specifically, the invention relates to designing a stage of an axial flow turbine for a gas turbine unit. Generally the turbine stator includes a vane carrier with slots where a row of vanes and a row of stator heat shields are installed one after another. The same stage includes a rotor having a rotating shaft with slots where a row of rotor heat shields and a row of blades are installed one after another.
2. Brief Description of the Related Art
This disclosure relates to a gas turbine of the axial flow type, an example of which is shown in FIG. 1. The gas turbine 10 of FIG. 1 operates according to the principle of sequential combustion. It includes a compressor 11, a first combustion chamber 14 with a plurality of burners 13 and a first fuel supply 12, a high-pressure turbine 15, a second combustion chamber 17 with a second fuel supply 16, and a low-pressure turbine 18 with alternating rows of blades 20 and vanes 21, which are arranged in a plurality of turbine stages arranged along the machine axis 22.
The gas turbine 10 according to FIG. 1 has a stator and a rotor. The stator includes a vane carrier 19 with the vanes 21 mounted therein; these vanes 21 are necessary to form profiled channels where hot gas developed in the combustion chamber 17 flows through. Gas flowing through the hot gas path 29 in the required direction hits against the blades 20 installed in shaft slits of a rotor shaft and causes the turbine rotor to rotate. To protect the stator housing against the hot gas flowing above the blades 20, stator heat shields installed between adjacent vane rows are used. High temperature turbine stages require cooling air to be supplied into vanes, stator heat shields, and blades.
A section of a typical air-cooled gas turbine stage TS of a gas turbine 10 is shown in FIG. 2. Within a turbine stage TS of the gas turbine 10, a row of vanes 21 is mounted on the vane carrier 19. Downstream of the vanes 21 a row of rotating blades 20 is provided each of which has at its tip an outer platform 24 with teeth (52 in FIG. 3(B)) arranged on the upper side. Opposite to the tips (and teeth 52) of the blades 20, stator heat shields 26 are mounted on the vane carrier 19. Each of the vanes 21 has an outer vane platform 25. The vanes 21 and blades 20 with their respective outer platforms 25 and 24 border a hot gas path 29, through which the hot gases from the combustion chamber flow.
To ensure operation of such a high temperature gas turbine 10 with long-term life span, all parts forming its flow path 29 should be cooled effectively. Cooling of turbine parts is realized using air fed from the compressor 11 of the gas turbine unit. To cool the vanes 21, compressed air is supplied from a plenum 23 through the holes 27 into the cavity 28 located between the vane carrier 19 and outer vane platforms 25. Then the cooling air passes through the vane airfoil and flows out of the airfoil into the turbine flow path 29 (see horizontal arrows at the trailing edge of the airfoil in FIG. 2). The blades 20 are cooled using air which passes through the blade shank and airfoil in vertical (radial) direction, and is discharged into the turbine flow path 29 through a blade airfoil slit and through an opening between the teeth 52 of the outer blade platform 24. Cooling of the stator heat shields 26 is not specified in the design presented in FIG. 2 because the stator heat shields 26 are considered to be protected against a detrimental effect of the main hot gas flow by the outer blade platform 24.
Disadvantages of the above described design can be considered to include, firstly, the fact that cooling air passing through the blade airfoil does not provide cooling efficient enough for the outer blade platform 24 and thus its long-term life span. The opposite stator heat shield 26 is also protected insufficiently against the hot gas from the hot gas path 29.
Secondly, a disadvantage of this design is the existence of a slit within the zone A in FIG. 2, since cooling air leakage occurs at the joint between the vane 21 and the subsequent stator heat shield 26, resulting in a loss of cooling air, which enters into the turbine flow path 29.